Diseases that affect vision can be treated with a variety of therapeutic agents, but the delivery of drugs to the eye continues to be challenging. Injections of therapeutic via the eye can be painful, involve some risk of infection, hemorrhage and retinal detachment. Depending on the frequency, intra-ocular injections can be time-consuming for both patient and physician. Consequently, in at least some instances the drug may be administered less often than the prescribed frequency resulting in sub-optimal treatment benefit. Further, bolus intra-ocular injections may not provide the ideal pharmacokinetics and pharmacodynamics. A bolus injection of drug into the vitreous humor of a patient can result in a peak drug concentration several times higher than the desired therapeutic amount and then before the patient is able to get the next injection drop to a drug concentration that is far below therapeutic effectiveness.